The goal of this research is to elucidate the neural control of vomiting, an event commonly associated with motion and radiation sickness, poisoning, and pregnancy. An initial objective will be to study in cats the brainstem projections to the muscles (abdominal and diaphragm) that are primarily responsible for producing the pressure changes required for vomiting. A longer term objective will be to establish the inputs to these brainstem areas that may produce vomiting under various conditions. It is unknown whether vomiting is produced via descending brainstem respiratory neurons that affect abdominal and phrenic motoneuronal activity or by way of other descending systems or both. Specific aims include establishing whether respiratory-spinal neurons participate in the control of vomiting by determining if they maintain their normal rhythm or fire in phase with co-active abdominal and phrenic nerves during fictive vomiting in paralyzed, decerebrate cats. Other, non-respiratory brainstem areas that may control abdominal muscle activity will be identified by retrograde transport of horseradish peroxidase (HRP) injected into the upper lumbar ventral horn. HRP will also be used to locate the phrenic motoneurons that innervate the inner hiatal region of the diaphragm encompassing the esophagus; these fibers become inactive during expulsion in contrast to the rest of the diaphragm. The next aim will be to determine if there are separate brainstem projections to the parts of the phrenic motor pool that innervate these different areas of the diaphragm, using HRP and electrophysiological techniques. It will also be established whether any descending brainstem neurons that are active during fictive vomiting project to the region of both phrenic and abdominal motor pools and may thus cause the co-activation of the diaphragm and abdominal muscles that occurs during vomiting.